High pressure reaction vessel for quality control of diamond growth on diamond seed

ABSTRACT

Improvements are provided in reaction vessel construction used in the growth of diamond by the process disclosed in U.S. Pat. No. 3,297,407 -- Wentorf, Jr. In assembly of the reaction vessel of this invention, the plug of catalyst-solvent material is disposed between the source of carbon and the diamond seed material as in the Wentorf, Jr. patent and, in addition, the diamond seed material is separated from the catalyst-solvent plug by means for isolating the diamond seed material from the catalyst-solvent material until after the latter has become saturated with carbon from the source of carbon. In addition, preferably the under surface of the plug of catalyst-solvent metal is covered with means for suppressing diamond nucleation. The nucleation suppressing means is usually in the form of a disc and may completely cover the underside of the catalyst-solvent plug or may have a hole therethrough in juxtaposition to the diamond seed/isolating means combination(s). When both the isolating means and the nucleation suppressing means are employed, capability is provided for simultaneously preventing dissolution of the diamond seed and suppressing spurious diamond nucleation.

This is a division of application Ser. No. 412,425 filed Nov. 2, 1973now U.S. Pat. No. 4,034,066.

BACKGROUND OF THE INVENTION

The synthesis of diamond crystals by high pressure, high temperatureprocesses has become well established commercially. Preferred methodsfor making diamonds are disclosed and claimed in U.S. Pat. Nos.2,947,610 -- Hall et al and 2,947,609 -- Strong. Apparatus for theconduct of such processes is described and claimed in U.S. Pat. No.2,941,248 -- Hall. The Hall et al, Strong and Hall patents areincorporated by reference.

Diamond growth in the aforementioned processes occurs by the diffusionof carbon through a thin metallic film of any of a series of specificcatalyst-solvent materials. Although such processes are verysuccessfully employed for the commercial production of industrialdiamond, the ultimate crystal size of such diamond growth is limited bythe fact that the carbon flux across the catalyst film is established bythe solubility difference between graphite (the typical startingmaterial) and the diamond being formed. This solubility difference isgenerally susceptible to significant decrease over any extended perioddue to a decrease in pressure in the system and/or poisioning effects inthe graphite being converted.

On the other hand, in the method of growing diamond on a diamond seedcrystal disclosed in U.S. Pat. No. 3,297,407 -- Wentorf, Jr.(incorporated by reference) a difference in temperature between thediamond seed and the source of carbon is relied upon to establish aconcentration gradient in carbon for deposition on the seed.Catalyst-solvents disclosed in the aforementioned Hall et al and Strongpatents are used in the temperature gradient method as well. The growthof diamond on the seed material is driven by the difference insolubility of diamond in the molten catalyst-solvent metal at thenutrient (source of carbon) and at the seed, between which locations atemperature gradient exists. Most important, this general type ofreaction vessel configuration presents a pressure stable system so thatpressure can more readily be kept in the diamond stable region.

By very carefully adjusting pressure and temperature and utilizingrelatively small temperature gradients with extended (relative to growthtimes for thin film method) growth times, larger diamonds can beproduced by the method as taught in the Wentorf patent than by thethin-film method.

Attempts to reliability produce very high quality diamond growth,however, have presented at least two apparently mutually exclusive, yetsimultaneously occurring problems. These problems are:

a. the strong tendency for spontaneous nucleation of diamond crystalsnear the diamond seed material (which occurs with increase in thetemperature gradient over the "safe" value); if the growth period isextended to produce from the seed diamond growth of greater than about1/20 carat in size the nucleated growth competes with the growthproceeding from the diamond seed with subsequently occurring collisonsof multiple crystals that result in stress fractures therein, and

b. either partial or complete dissolution of the diamond seed materialin the melted catalyst-solvent metal during that part of the process inwhich the catalyst-solvent medium becomes saturated with carbon from thenutrient source and then melts; such dissolution produces uncoordinateddiamond growth proceeding from spaced loci, which growths upon meeting,result in subsequent confused, flaw-filled growth.

SUMMARY OF THE INVENTION

The instant invention provides an improvement over the inventiondisclosed in Wentorf, Jr. making possible the simultaneous solution ofeach of problems (a) and (b) set forth above and enabling the productionof large diamond crystals having purities and freedom from flawsextending to the degree of perfection recognized as characteristic ofgem quality. Thus, examples are given herein of diamonds produced inaccordance to the teachings of this invention that are without internalflaws when viewed under a corrected magnifier of not less than 10 power.Some of these same diamonds have been graded as having a rating in theH-J range in the GIA Color-Grading System page 308 of The DiamondDictionary, Copyright 1960, Gemological Institute of America!.

In the reaction vessel construction of the instant invention, asassembled, the body of catalyst-solvent metal is separated from hediamond seed material by means for isolating the diamond seed materialfrom the catalyst-solvent material until after the latter has becomesaturated with carbon from the source of carbon. Preferably, thisisolating means is a barrier layer of a metal selected from a list ofspecific metals set forth hereinbelow.

In addition to the aforementioned isolating means, means for suppressingdiamond nucleation may be disposed as a layer, or disc, in contact withand covering the underside of the mass of catalyst-solvent metal. Thelayer of diamond nucleation suppressing means is preferably made of amaterial selected from a specific list of material also set forthhereinbelow.

When both a barrier layer and a nucleation suppression layer are used inany given reaction vessel construction, the materials of which theselayers are made differ from each other and from the catalyst-solventmass employed. In any event the metal selected for the barrier layermust have a melting point, when it is in contact with diamond, that ishigher than the melting point of the metallic catalyst-solvent, when thecatalyst-solvent is both (a) saturated with carbon dissolved therein and(b) in contact with diamond.

BRIEF DESCRIPTION OF THE DRAWING

This invention will be better understood from the following descriptionand drawing in which:

FIG. 1 illustrates one exemplary high pressure, high temperatureapparatus useful in the practice of this invention;

FIG. 2 illustrates in an enlarged view one reaction vessel constructionassembled in accordance with this invention;

FIG. 3 is an even larger scale view of the vicinity of the diamond seedmaterial shown in FIG. 2; or

FIGS. 4, 5, 6, 7 and 8 are large scale views of the vicinity of thediamond seed material as this region would appear in three variations ofthe construction shown in FIG. 2 and

FIG. 9 shows the relation between new diamond growth, the diamond seedand the catalyst-solvent bath.

DESCRIPTION OF THE PREFERRED EMBODIMENT

One preferred form of a high pressure, high temperature apparatus inwhich the reaction vessel of the instant invention may be employed isthe subject of the aforementioned U.S. Pat. No. 2,941,248 -- Hall and isschematically illustrated in FIG. 1.

In FIG. 1, apparatus 10 includes a pair of cemented tungsten carbidepunches 11 and 11' and an intermediate belt or die member 12 of the samematerial. Die member 12 defines a centrally-located aperture and incombination with the punches 11, 11' defines a pair of annular volumes.Between punch 11 and the die 12 and between punch 11' and the die 12there are included gasket/insulating assemblies 13, 13', each comprisinga pair of thermally insulating and electrically non-conductingpyrophyllite members 14 and 16 and an intermediate metallic gasket 17.The aforementioned assemblies 13, 13' together with end cap assemblies19, 19' and electrically conductive metal end discs 21, 21' serve todefine the volume 22 occupied by reaction vesel 30. Each end capassembly comprises a pyrophyllite plug, or disc, 23 surrounded by anelectrically conducting ring 24.

Reaction vessel 30 (FIG. 2) is of the general type disclosed in U.S.Pat. No. 3,030,662 -- Strong (incorporated by reference) modified by theaddition of steel retaining rings 31 and 32. Hollow cylinder 33 ispreferably made of pure sodium chloride, but may be made of othermaterial such as talc.

Broad criteria for the selection of the material for cylinder 33 arethat the material (a) not be converted under pressure toa stronger andstiffer state as by phase transformation and/or compaction and (b) besubstantially free of volume discontinuities appearing under theapplication of high temperatures and pressures as occurs, for example,with pyrophyllite and porous alumina. The materials meeting the criteriaset forth in U.S. Pat. No. 3,030,662 (column 1, line 59 through column2, line 2) are useful for preparing cylinder 33. Positionedconcentrically within and adjacent cylinder 33 is a graphite electricalresistance heater tube 34. Within graphite heater tube 34 there is inturn concentrically positioned cylindrical salt liner plug 36 upon whichare positioned hollow salt cylinder 37 and its contents.

Operational techniques for applying both high pressures and hightemperatures in this apparatus are well known to those skilled in theart. The foregoing description relates to merely one high pressure, hightemperature apparatus. Various other apparatuses are capable ofproviding the required pressures and temperatures that may be employedwithin the scope of this invention. Pressures, temperatures, metalliccatalyst-solvents and calibrating techniques are disclosed in theaforementioned patents incorporated by reference.

The bottom end of cylinder 37 encloses the embedment disc 38 having atleast one diamond seed 39 embedded therein. If a plurality of diamondseeds they would be located in spaced locations with one at eachlocation. Diamond seeds are preferably 1/4 to 1/2 mm in size and havinga cube face, but diamond may be seeded from any face. Preferably, all ofthe underside of plug 41 of metallic catalyst-solvent is covered withmeans for suppressing diamond nucleation over a preselected area (e.g.disc, or layer, 42) except, perhaps for a hole therethrough as shown inFIGS. 4-8. Isolating means are always initially disposed between diamondseed 39 and the direction by which molten catalyst-solvent will move toreach seed 39 in order to prevent premature contact therebetween such aswould result in dissolution (partial or complete) of seed 39. The uppersurface of diamond seed material 39 should be oriented with awall-formed face e.g. a cube face in contact with the underside of metaldisc 43. Also located within salt cylinder 37 are the nutrient supply 44and salt cylinder 46 disposed thereover.

Pressure-transmitting members 36, 37, 38 and 46 are made of materialmeeting the same criteria as the material for cylinder 33. All of parts33, 36, 37, 38 and 46 are dried in vacuum for 24 hours at 124° C beforeassembly. Other combinations of shapes for the pressure-transmittingmembers 36, 37, 38 and 46, may, of course, be employed. However, thearrangement of these parts shown in FIG. 2 has been found to be the mostconvenient to prepare and assemble.

When reaction vessel 30 is disposed in space 22, heater tube 34 formselectrical contact between end discs 21, 21' so that heat may becontrollably applied during conduct of the process.

Seed isolation disc (barrier layer) 43 is preferably made of platinumbut may be made of a metal selected from any of the metals in the groupconsisting of platinum, molybdenum, titanium, tantalum, tungsten,iridium, osmium, rhodium, palladium, vanadium, ruthenium, chromium,hafnium, rhenium, niobium and zirconium and alloys of these metals. Bypreventing damage to the exposed seed face the isolation or barriermetal prevents the occurrence of diamond growth from more than one locuson the seed face. To insure requisite isolation, disc 43 is unpierced,at least where it is in contact with the diamond seed material. Whensuch protection is not provided, erosion of the diamond seed materialoccurs. Considering a given diamond seed the erosion may eithercompletely or partially destroy the seed. In the former case diamondnucleation can occur at spaced loci at the underside of thectalyst-solvent mass and in the latter case diamond growth usuallyproceeds from different loci on the eroded seed. Resultant new diamondgrowth in either case is lacking in coordination between the multiplegrowth and many flaws develop at the interface(s) when these separategrowths meet.

In any given reaction vessel construction different materials areemployed for each of (a) the catalyst-solvent material, (b) the barrierlayer and (c) the nucleation suppressing layer. Nucleation suppressinglayer 42 is selected from the group consisting of cobalt, iron,manganese, titanium, chromium, tungsten, vanadium, niobium, tantalum,zirconium, alloys of the preceeding metals, mica, polycrystallinehigh-density alumina, powdered alumina, quartz, silica glass, hexagonalboron nitride crystals, cubic boron nitride crystals, wurtzite-structureboron nitride crystals and silicon carbide protected with one of themetals of the platinum family. Preferably, in the last instance siliconarbide particles are mixed with an inert material such as sodiumchloride and formed as a solid disc having the upper surface thereof (incontact with the underside of plug 41) covered with a thin layer of oneof the platinum family metals.

When disc 42 is made of mica, polycrystalline high-density alumina,quartz, silica glass or other material presenting a layer with which themolten catalyst-solvent system will not alloy and/or cannot penetrate,it is necessary to provide a hole (as shown in FIGS. 4-8) through disc42 to accommodate contact between the molten catalyst-solvent bath anddisc 43 for eventual contact with seed 39. Disc 42 may, of course, beprovided with a hole when made of metal, if desired.

The nutrient material 44 may be composed of diamond, diamond plusgraphite or may be entirely of graphite, if desired. In the case ofdiamond plus graphite, the graphite occupies any void space. It ispreferred that the nutrient contain mostly diamond in order to reducethe volume shrinkage tht can result during conduct of the process. Inconduct of the process any graphite present at operating temperaturesand pressures converts to diamond before going into solution in thecatalyst-solvent metal. Thus, the pressure loss is minimized so that theoverall pressure remains in the diamond-stable region at the operatingtemperature.

When a nucleation suppressing layer 42 is employed, enough of thesurface of the underside of catalyst-solvent metal plug 41 is covered bythe layer to provide an environment adjacent the seed 39 in whichspontaneous diamond nucleation will be suppressed for a considerabledistance around diamond seed 39. Thus, the entire underside of plug 41may be covered by layer 42, but if less than the entire surface iscovered, the layer 42 should extend at least 50% more distance from theseed than the lateral growth dimension desired. If the disc 42 is madeof one of the metallic materials listed above, some space must existbetween the diamond seed 39 and the closest portion of disc 42 intowhich the material of disc 38 will extend. When layer 42 is a metal andis provided with a hole, the ratio of diameter of hole to largestdimension of seed 39 should be in the range of 1.5:1 to 5:1. When layer42 is composed of mica, the hole is preferably much smaller than theseed, e.g. as small as 0.001 to 0.020 inch. This has effect of makingthe seed presented to the catalyst-solvent bath vary small, leading togreater perfection of seeding and growth.

The exact mechanism (or mechanisms) by which discs, or layers, of thediamond nucleation suppressor materials function to reduce or eliminatediamond nucleation is not known for certain.

In the case of the isolation means for the diamond seed material (disc43) physical contact between the catalyst-solvent metal and the diamondseed is prevented until after the catalyst-solvent metal 41 has beenmelted and become saturated with carbon from the nutrient mass 44. Thetiming is such that this carbon saturation occurs before barrier layer43 is dissolved by the molten catalyst-solvent. Once barrier layer 43becomes dissolved in the molten catalyst solvent the exposed face of thediamond seed 39 sets the pattern of growth and development of the newgrowth may proceed.

The thickness of the nucleation suppressing layer 42, when used, shouldrange from about 1 to about 10 mils while the thickness of the sedisolation disc 43 should range from about 1/2 to about 10 mils. Whennatural mica, e.g. muscovite is employed, the disc should first be firedat about 800° C for 12-15 hours. The preferred thickness of mica isabout 2-3 mils.

Even those isolation disc materials listed which form carbides that arestable with respect to diamond at the pressures and temperaturesemployed function well since the carbide forming process is slowcompared to the speed with which the pool of catalyst-solvent metalbecomes saturated with carbon. Any carbide formed eventually dissolvesin the pool of catalyst-solvent metal. There was no evidence thatplatinum formed a carbide more stable than diamond.

FIGS. 4-8 show alternate arrangements for the nucleation suppressingdisc/barrier disc/diamond seed combination. In each case the balance ofthe reaction vessel construction not shown is the same as is representedin FIG. 2. The same numerals represent the same items of constructionserving identical functions in the several views.

In each of FIGS. 4 and 5 a projecting portion of embedment disc 38presents barrier layer 43 into contact with the underside of mass 41 ofcatalyst-solvent. Embedded seed 39 is disposed directly under disc 43with a single face thereof in direct contact with disc 43. In FIG. 5,isolating layer 43 extends below the nucleation suppressing layer 42beyond the edge of hole 42'. In FIG. 4 the material of which disc 38 iscomposed should separate seed 39 from the wall(s) of hole 42'. Thus, inthe case of the arrangements of FIGS. 4 and 5, when nucleationsuppressing disc 42 is non-metallic (and a cube face of seed 39 isoffered as "template" for the new diamond growth), the relationshipbetween the diamond seed and new growth 47 will be as shown in FIG. 9.It is advantageous not to have the new growth envelope the seed at all,because much less of the new growth will need to be polished away toremove flaws.

The arrangement shown in FIGS. 3 and 6 enable the production of newdiamond growth as shown in FIG. 9, when nucleation suppressing layer 42is metallic and thereby dissolved by the molten catalyst-solvent. Aspreviously mentioned the growth configuration shown develops when a cubeface of seed 39 is in contact with barrier layer 43. Projection 41' ofthe catalyst-solvent fits closely to the wall(s) of hole 42' andprojects through hole 42' to contact barrier layer 43 over seed 39.

The advantage of using both the barrier layer and the nucleationsuppressing layer may be assessed as follows. When only the barrierlayer is employed about 70% of the attempts to grow single, large, highquality diamonds will encounter spontaneous diamond nucleation andinterference with growth of the new diamond growth from the seed.Sometimes this interference is not serious, but most often the growthfrom the seed is badly damaged. When a nucleation suppressing layer isused the improvement is so dramatic that only about 30% of the attemptsto grow single, large, high quality diamonds will encounter spontaneousdiamond nucleation. In fact, since the use of natural mica has beeninstituted, spontaneous diamond nucleation has not occurred in a singleinstance.

The arrangements of FIGS. 7 and 8 are useful, when solid non-metallicnucleation suppressing layer materials such as mica or machinablealumina are employed. In each case a small hole 48 is drilled or punchedthrough disc 42. This hole is preferably in the range of from 0.001 to0.020 inch in diameter. In the arrangement of FIG. 7, when thecatalyst-solvent material 41 becomes molten, it passes through hole 48and, after a period of time, alloys with the melts isolation disc 43thereby reaching diamond seed 39 to intitiate diamond growth back upthrough hole 48 to provide seeding for diamond growth above layer 42. Inthe arrangement of FIG. 8 a wire 49 occupies hole 48. The wire may, forexample, be of nickel, Fe-Al or Fe-Ni alloy and extends through disc 42to contact both plug 41 and isolation barrier 43. As thecatalyst-solvent material 41 and then the material of wire 39 becomemolten and carbon is dissolved therein, the isolating barrier 43 alloysand diamond growth begins for supplying a seed at the upper side oflayer 42.

The temperature differential between the hot part of the cell (abouthalf-way up the height of the cell) and the diamond pocket is preferablyin the range of 20°-30° C. This differential depends upon theconstruction of the cell e.g. depth of mass of metalliccatalyst-solvent, differential resistance in the heater tube, thermalconductivity of the end discs etc. Thus, the thickness of plug 41 helpsdetermine the temperature differential prevailing in the reactionvessel. With a thicker mass of catalyst-solvent the temperaturedifference is greater. Vertical location of plug 41 is alsodeterminative.

Gem quality diamonds have been produced in the practice of thisinvention in near colorless, clear light yellow and clear dark yellow."Colorless" is used interchangeably with "white" or "water white." Thenear colorless crystals are typical truncated octahedra with modifyingcube faces while the yellow stones are well-developed octahedra withminor truncations and with one point diminished. The latter shape isexcellent for high weight yield when cut as a round brilliant.

The near colorless stones rated H to J on the GIC Grading Scale, whichhas rating values ranging from D (colorless) to N (yellow). Occasionalinclusions of catalyst-solvent occur in the crystals as removed from theapparatus, but many of these can be cut away in the preparation of afashioned diamond.

Under 45× magnification these crystals may display minute whiteinclusions not visible under the 10× standard magnification used in thegrading of diamonds. These minute inclusions do not affect thebrilliance of the crystals and are not considered flaws.

The near colorless diamonds grown from a cube face phosphoresce afterexcitation by ultraviolet light (2537 A) with a characteristic patternin which a pair of non-phosphorescing linear bands in crossedrelationship appear in contrast to the balance of the crystal, whichphosphoresces. In contrast to those natural diamonds which phosphorescethese near colorless diamonds phosphoresce for a very long time, e.g. ofthe order of 1 hour. The phosphorescing diamonds are all low in nitrogencontent.

Although all natural stones having a rating of G or lower (progressingtoward N) on the GIA Color-Grading System have a large ultravioletabsorption band at about 4155 A, none of the near colorless H-J ratingdiamonds prepared according to this invention displayed such ultravioletabsorption band, i.e. these crystals give a substantially flat responsefrom 2250 A to greater than 4500 A. This phenomenon makes such stonesparticularly useful as spectrometer crystals for the monitoring ofradiation in the visible to ultraviolet range.

Further, the colorless diamonds in the H-J range (GIA scale) preparedaccording to this invention are good semi-conductors, when traces ofboron are present. More boron (about 1/4 ppm or more) starts to colorcrystal blue. The combination of crystal size (greater than 1/20 carat,particularly those greater than 1/5 carat), semiconductivity andnear-colorless clarity afforded by these diamonds and not observed innatural diamonds provides an excellent capability for the constructionof high pressure cells for the monitoring of absorption bands ofmaterials subject to the simultaneous application of high pressure andapplied voltage. Thus, such large, single-crystal near-colorlessdiamonds can be used as in-line windows for a high pressure cell formaking observations during the conduct of high pressure processes.

Also, apparently because of (a) the difference in nitrogen content and(b) the manner in which the nitrogen is present, near colorless diamondsproduced by the practice of this invention exhibit a much superiorthermal conductivity at temperatures in the range of about 10°-100° Kand abrasion resistance far in excess of that found in single crystalntural diamonds submitted to the grinding wheel abrasion test. Nitrogencontents of less than 10¹⁶ atoms of nitrogen per cm³ (less than 20 ppmof N) in the diamonds of this invention are particularly effective inincreasing both thermal conductivity and abrasion resistance.

Thus, the thermal conductivity of natural diamond did not exceed about120 watts/cm° K (at 80° K) while near colorless diamond of thisinvention had a value of 180 watts/cm° K) at the same temperature.

In the grinding wheel abrasion test abrasion resistnce quality (grindingratio) is taken as the volume of corundum (removed from a 60 gritcorundum wheel) in cubic inches removed per gram of diamond consumed.During the test the diamond is oriented with the most resistant grindingdirection the <110> direction on the cube face! against the wheel.During the test the in-feed to the corundum wheel was 0.001 inch foreach pass. Near colorless diamond according to this invention (less than20 ppm N content) displayed grinding ratios ranging from over 32,000 to200,000 in ³ /gm of diamond while colorless natural gave grinding ratiosranging from 12,000-64,000 in ³ /gm of diamond.

The near-colorless diamonds of this invention do not fluoresce underlong wave ultraviolet light (3660 A) however, under short waveultraviolet light (2537 A) these diamonds fluoresce strongly in tones ofyellow and green.

Therefore, it can be concluded that the low nitrogen content, nearcolorless (H to J on the GIA Grading Scale) diamonds of this inventionare superior to natural diamond for use as heat sinks at cryogenictemperatures and will provide more abrasion-resistant (and thereby moredurable) gem stones.

preferred catalyst-solvents for the practice of this invention are Fe,FeNi, FeNiCo, Fe-A1, Ni-Al, Fe-Ni-Al and Fe-Ni-Co-Al. Preferrednucleation suppressants are natural mica and cobalt and the preferredisolation barrier is platinum. When natural mica is used it should firstbe fired as directed hereinabove. When alloys of higher iron content areused, the diamonds produced have a lighter yellow color. With largeramounts of Ni and/or Co the resulting diamonds have a deeper yellowcolor.

For the reaction vesel construction described the preferred pressuresrange from 55-57 kilobars (kb) and preferred temperatures are in the1330°-1430° C range.

In each of the following examples the reaction vessel configurationprovided a temperature differential in the 20°-30° C range, the nutrientconsisted of 1 part by weight SP-1 (National Carbon Company) graphiteand 3 parts by weight 325 mesh diamond prepared by the thin film method,seeds used were 1/4 to 1/2 mm and temperatures were measured using aPt/Pt 10 Rh thermocouple:

                  EXAMPLE 1    ______________________________________     Run 102!    ______________________________________    Pressure           57 kb    Temperature (13.2 mv.)                       1340-1360° C    Catalyst           51Ni49Fe    Nutrient           210 mgm    Nucleation Suppressing Layer                       5 mil Fe disc                       covering all of                       bottom of                       catalyst-solvent                       mass    Isolation Barrier  5 mil Ta disc co-                       extensive and                       contiguous with                       Fe disc    Seed Arrangement   5 seeds in spaced                       relation in con-                       tact with Ta disc    Time               22 hours 40 min    ______________________________________

Four yellow crystals were produced, one growing from each of four seeds.One seed produced a cluster. The new diamond growth varied in size from10-20 mgm (1/20-1/10 carat). The crystals had small inclusions near oneface but were otherwise clear. In each case the crystal habit wascubo-octahedral with modifying cube faces.

                  EXAMPLE 2    ______________________________________     Run 19!    ______________________________________    Pressure           57 kb    Temperature (13.9 mv)                       1400-1420° C    Catalyst           51Ni49Fe    Nutrient           210 mgm    Nucleation Suppressing Layer                       none    Isolation Barrier  1 mil W disc covering                       all of bottom of                       mass of catalyst-                       solvent    Seed Arrangement   5 seeds in spaced                       relation in contact                       with W disc    Time               5 hours    ______________________________________

Five light yellow crystals resulted, one developed from each seed. Thenew growth had an average size of 1.52 mgm and each measured about 1 mmalong a cube face. The crystals were well-formed, clear and relativelyfree of inclusions. In each case the crystal was cubo-octahedral withmodifying cube faces.

With multiple seeding the requirement for nucleation suppression isreduced and with proper operating conditions and a seed populationdensity of 1 seed/8-10 mm² the nucleation disc can be dispensed with.

                  EXAMPLE 3    ______________________________________     Run 70!    ______________________________________    Pressure           56 kb    Temperature (13.4 mv)                       1360-1380° C    Catalyst           51Ni49Fe    Nutrient           450 mgm    Nucleation Suppressing Layer                       5 mil Co disc with                       150 mil dia. hole    Isolation Barrier  1 mil Pt disc as in                       FIG. 4    Seed Arrangement   as in FIG. 4    Time               67 hours    Weight of Diamond Growth                       213 mgm    ______________________________________

The seeded diamond growth was yellow and of gem quality. Three othervery small crystals grew out of the region occupied by the seededgrowth. Crystal shape was truncated octahedron with modifying cubefaces.

                  EXAMPLE 4    ______________________________________     Run 64!    ______________________________________    Pressure           57 kb    Temperature (13.3-13.6 mv)                       1360-1400° C    Catalyst           51Ni49Fe    Nutrient           400 mgm    Nucleation Suppressing Layer                       5 mil Fe disc (FIG. 3)    Isolation Barrier  5 mil Mo disc (Fig. 3)    Seed Arrangement   as in Fig. 3    Time               85 hours    Weight of Diamond Growth                       190.4 mgm    ______________________________________

A single beautiful yellow gem crystal developed. The crystal shape wascubo-octahedral.

                  EXAMPLE 5    ______________________________________     Run 58!    ______________________________________    Pressure           56 kb    Temperature (13.7 mv)                       1390-1405° C    Catalyst           51Ni49Fe    Nutrient           400 mgm    Nucleation Suppressing Layer                       5 mil Co disc with                       150 mil diameter                       hole    Isolation Barrier  1 mil Pt disc in the                       150 mil diameter                       hole    Seed Arrangement   as in FIG. 4    Time               683/4 hours    Weight of Diamond Growth                       156 mgm    ______________________________________

A single beautiful golden yellow gem was produced in a cubo-octahedronshape with modified octahedral edges.

                  EXAMPLE 6    ______________________________________     Run 42!    ______________________________________    Pressure           56.5 kb    Temperature (13.2 mv)                       1345-1360° C    Catalyst           Fe + 3 wt.% Al    Nutrient           500 mgm    Nucleation Suppressing Layer                       None    Isolation Barrier  1 × 20 × 20 mils Pt                       disc    Seed Arrangement   as in FIG. 4    Time               160 hours    Weight of Diamond Growth                       206 mgm    ______________________________________

A single beautiful, near colorless crystal was grown. Crystal shape wastruncated cubo-octahedron with modifying cube faces; phosphoresces over1 hour after exposure to 2537 A light; gives high substantially flattransmission of ultraviolet light from about 2250 A - 3.30 μ and from6.00 μ to 50 μ; is semi-conducting and thermoluninesces. The thermalconductivity of the crystal at 80° K was at least 180 watts/cm° K.

                  EXAMLE 7    ______________________________________     Run 50!    ______________________________________    Pressure           as in Example 6    Temperature (13.2 mv)                       as in Example 6    Catalyst           as in Example 6    Nutrient           as in Example 6    Nucleation Suppressing Layer                       none    Isolation Barrier  1 × 20 × 20 mils Pt                       disc    Seed Arrangement   as in FIG. 4    Time               161 hours    Weight of Diamond Growth                       256 mgm    ______________________________________

In addition to the seeded growth one other small (22 mgm) diamondcrystal grew and interfered slightly with seeded growth, which wascolorless and gem quality. The flaws were polished out to produce a 194mgm crystal. The crystal possessed properties of phosphorescence,ultraviolet transmission, electrical conductivity, thermal conductivityand thermoluminescence as in Example 6. Abrasion resistance was veryhigh. Since very small amounts of diamond are removed in making thegrinding wheel abrasion test, measurements are difficult to makeaccurately when large amounts of corundum are removed. Test resultsproduced grinding ratios ranging from 120,000 to 168,000 in ³ /gm ofdiamond seed.

                  EXAMPLE 8    ______________________________________     Run 198!    ______________________________________    Pressure           55 kb    Temperature        1300° C    Catalyst           95Fe5Al (prealloyed)    Nutrient           500 mgm    Nucleation Suppressing Layer                       2 mil natural mica                       (fired) disc with                       7 mil diameter                       hole    Isolation Barrier  1 × 20 × 20 mils                       Pt disc    Seed Arrangement   as in FIG. 7    Time               190 hours    Weight of Diamond Growth                       140 mgm    ______________________________________

A single, nearly-flawless crystal was formed. The crystal was in theshape of a truncated octahedron. In addition to the (111) faces, thecrystal had cube faces (100), dodecahedron faces (110) and (113) faces.

Experiments have verified the lack of utility of snythetic mica,platinum, nickel and molybdenum as nucleation suppressing materials.

After termination of each run and reduction of temperature and pressureto permit removal of the reaction vessel 30, the new diamond growthembedded in the solidified metallic catalyst-solvent 41 readily detachesfrom the seeding site(s). The diamond(s) so prepared is easily removedby breaking open the mass 41. Designations of the diamond seed areschematic and no attempt has been made to show the preferreddisposition.

The crystals resulting from the practice of this invention develop insymmetries determined by the face of the seed crystal selected as thepattern. Thus, a diamond crystal grown from a cube face (100) of theseed crystal will be symmetrical about the cube axis and, in the case ofnear colorless diamonds, such a crystal will result in the uniquepattern of phosphorescence described hereinabove. Although crystalssymmetrical about other axes can be formed using other faces of the seedcrystal e.g. (110), (111), (113)! to set the growth pattern, diamondssymmetrical about the cube axis yield the most crystal and are of thebest quality for a given reaction cell volume during a given growthtime. It is an important feature of this invention that the seed crystalsets the growth pattern for, but does not become part of, the newdiamond growth thereby assuring symmetrical growth without having theinterior obscured as by the presence of a seed.

What we claim as new and desired to secure by Letters Patent of theUnited States is:
 1. In a diamond synthesis reaction vessel forintroduction into the reaction volume of a high pressure, hightemperature apparatus, said reaction vessel constituting an assembly ofinterfitting elements for enclosing diamond seed material and a sourceof substantially pure carbon, said diamond seed material and source ofcarbon being separated by a mass of metallic catalyst-solvent materialfor the diamond-making reaction disposed therebetween so as to provide apredetermined temperature gradient between said diamond seed materialand said source of carbon under operating conditions of pressure andtemperature in the diamond stable region of the phase diagram of carbon,said diamond seed material and said source of carbon being located inseparate regions of said reaction vessel such that under said operatingconditions said diamond seed material will be heated to a temperaturenear the minimum value of temperature for said temperature gradient andsimultaneously said source of carbon will be heated to a temperaturenear the maximum value of temperature for said temperature gradient, thecombination with said interfitting elements ofa. a layer of metallicisolating material disposed in contact with the diamond seed materialand between said diamond seed material and the mass of catalyst-solventmaterial, said isolating material being unpierced where contact is madewith said diamond seed material and being selected from the groupconsisting of platinum, molybdenum, titanium, tantalum, tungsten,iridium, osmium, rhodium, palladium, vanadium, ruthenium, chromium,hafnium, rhenium, niobium and zirconium and alloys thereof and in anygiven reaction vessel construction said isolating material having amelting point, when in contact with diamond, that is higher than themelting point of the metallic catalyst-solvent material saturated withcarbon dissolved therein when in contact with diamond.
 2. Thecombination recited in claim 1 wherein the diamond seed material is asingle crystal.
 3. The combination recited in claim 2 wherein thediamond seed is oriented with a cube face thereof in contact with theisolation layer.
 4. The combination recited in claim 1 wherein thediamond seed material consists of single crystals at spaced locations.